Patent GB-820413-A (GB)
Title: Improvements relating to photographic cameras
Inventor: RUSSELL LIONEL VIVIAN FRANK
IPC: G03B19/04
Filed: 1956-09-14
Abstract: 820,413. Photographic cameras. AERONAUTICAL & GENERAL INSTRUMENTS Ltd. Sept. 11, 1957 [Sept. 14, 1956], No. 28186/56. Class 98(1) In a roll film camera, a rotatable annular plate coaxial with the lens housing carries a manually operable control member which is movable from a rest position to a shutter release position, further motion in the same direction serving to reset the shutter and wind on the film, the plate being returnable to its rest position only after the operations are completed. As shown, upon rotation of an annular cam plate 8 through a small angle counter-clockwise from its rest position by means of a control lever 10, a pawl 12 trips a shutter release mechanism of known type within the lens housing 6. During exposure a pin 20 on the lever 22 rides in the constant radius part 16 of the slot 18, and after completion of exposure enters the radially inclined portion of the slot to cause pivoting of the lever 22 and hence resetting of the shutter mechanism by co-operation with the latter of the ledge 24. A film driving pawl 26 pivotally mounted on the plate 8 and radially inwardly urged by spring force projects into the end 34 of one of four recesses 28 on the inner face of a crown wheel 30 in the rest position of the system; during the initial rotation of the cam plate 8, the pawl moves from one end of the recess 28 to other and after exposure has taken place the end 36 of the recess is engaged resulting in rotation of the crown wheel 30 which meshes with the toothed wheel 28 to drive the film advancing sprocket 44. The take up spool 52 which is provided with a free wheel 50 is driven by means of a slipping drive belt 48 so that the spool is overdriven to maintain the film taut. The cam plate is returned to its initial position after the three operations have been performed by means of a spring 54 mounted on a coaxial fixed ratchet plate 58 and having one end attached to the latter at 60, the other end is attached to a lever 62 pivoted to the cam plate 8 such that during the initial rotation thereof, the lever 62 pivots without stretching the spring; thereafter pivoting ceases and the spring flexes proportionally to the rotation thus enabling the operators to sense when the exposure part of the cycle is complete. The ratchet plate 58 has a recess 74 at its periphery, part of which contains ratchet teeth 76 such that if the lever 10 is released before the film has been wound on one complete frame, the pawl 26 rides down the rim 78 and engages behind one of the ratchet teeth, but if the correct winding has been achieved, the member 26 slides down the rim 78 in the neighbourhood of 74 where there are no teeth and slides up the adjacent rim 79 and over the periphery into the next recess 28. A further pawl 80 riveted to the cam plate 8 rides over the surface of a fixed plate 84 and near the end of its path protrudes through an aperture 88 to co-operate with one of the holes 86 in a coaxially mounted plate 85 to rotate the latter to indicate the number of exposures through a window in the camera housing.